1. Field of the Invention
This invention relates to temperature measuring devices, and in particular, to a temperature measuring device having a plurality of sensors therein.
2. Descriptionof of the Prior Art
As is well known to those skilled in the art of temperature measurement, there are times when it is necessary to measure the temperature at several predetermined points along a predetermined line of investigation leading to the interior of a body, for example, a steam turbine pressure containment vessel. Such investigation may be needed in order to determine the radial temperature distribution within the turbine pressure vessel, and, it is therefore necessary to measure the temperature within the casing at several points along the line of investigation. Frequently, the temperature variation along the line of investigation is accompanied by variations in the other direction surrounding that predetermined line. For example, when measuring the radial temperature distribution, it is found that the radial variation in temperature is often accompanied by axial and circumferential variations as well. Because of these gradients in temperature, it is necessary to confine the measurement to a very localized region surrounding the line of interest. In addition, the measuring devices themselves must not introduce appreciable disturbances to the basic temperature field. For example, the devices must not introduce large empty cavities within the body which tend to distort the temperature fields therein. Also, the measuring device utilized must be placed in an intimate, temperature sensing relationship with the body to be measured.
In the prior art, the most common solution to the above described problem has been to produce several individual holes of varying depth around the particular line of investigation, and to insert a separate temperature measuring device into each hole in order to measure the temperature at the bottom of each cavity. These individual readings, although they are somewhat displaced from the particular line of investigation, are considered estimates of the actual temperatues along that line.
This solution is unsatisfactory for several reasons. If appreciable temperature gradients exist around the line of interest, misleading temperature readings are obtained. Also, there are certain situations when it would be undesirable to introduce multiple cavities into the body being measured. For example, it may be undesirable to place a number of varying depth holes into a pressure vessel for a turbine apparatus since such holes tend to weaken the pressure vessel.
Another solution to the problem of measuring temperatures at a predetermined number of points along a line of investigation has been to prepare a single cavity extending into the interior of the body and to weld small flexible shims containing thermocouple elements to the boundary of the cavity at each point where the temperature is desired. In addition to the obvious difficulty and special skill and equipment required to effect this method of attachment, the operation produces weld effects which may be undesirable. Also, considerable distortion results in the thermal field because a fairly large cavity within the body member is left unfilled except for the shims and the sheath wires. In addition, the thermocouple wires are electrically grounded to the body member being measured and thus the possibility of spurious readings occurring due to extraneous electrical currents is increased.
It is apparent that a temperature measuring device able to accurately sense temperature at a predetermined number of points along a single line of investigation within a body member is needed. Further, a temperature measuring device which can make the plurality of required readings without introducing large void spaces within the body to disrupt the thermal field therein and which places the sensing elements in intimate temperature sensing relationships with the body is necessary.